I would just say your dps is low, I wouldnt say suck but low. If its low and it's still low after someone tell you nicely its low and need to fix the rotation, that one is on you.
My thoughts. Problem with the parser is, yes someone will abuse the living shit out of it and probably mock players they are bad. Keep in mind no one is perfect and everyone can improve each time they play, well for those who think it's fun being better and knowing their class and play it optimized. Then you have the players who are playing bad but willing to play better so they are willing to take tips and guides from other players (mad respect to those btw, met few of them and I'm so happy you take advice and willing to get better). Then you have those who are going to say, don't be mean, otherwise I will be sad or rage at you. Problem is, yes I do know there are people who will tell you to fuck off sadly because your dps is low, that is wrong, however people should tone it down and say, yes you need to somehow fix your dps and maybe rotation? Like opener and the actuall rotation after an opener? Many times I've sad that to players and oh boy the amazing feedback I get. Not only did they increase their dps, they are soo much more happy knowing they pulling off amazing dps and helping the group, yes by playing your class very very good!
Then you have those who are simply telling me to fuck off and say it's their sub and game. What's most toxic? The guy who tells you in a nice way how to improve your dps in a nice manner way, even putting time to show you them your own rotation, or the player who simply tells you to fuck off?
I got my own opinion right there but I simply won't say it as it should be obvious. Either way sorry for the derail on topic, I wish there was a parser built in game but honestly a personal one would be better simply because it will be mostlikely less harrasment but then again how can we excactly know if they are doing bad or not? There is a big chance many will use it but then wont care they do bad, that's a risk too.